1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a PCMO deposition process that forms a void-free interface with an underlying noble metal substrate.
2. Description of the Related Art
Pr1-XCaXMnO3 (PCMO) thin films have been found to have unique resistance change properties. With the application of a narrow nanosecond pulse, having an amplitude of 5 volts and a duration of 100 nanoseconds, the resistance can be changed to a high resistant state. Likewise, if a wider microsecond pulse is applied, the resistance can be reset to its initial (low-resistance) state. The observed change in resistance states is in the range of one to three orders of magnitude. Further, a resistance state changes can be affected in a PCMO film with the application of an opposite amplitude polarity narrow (nanosecond range) pulses. Thus, the resistance state of the PCMO film can be controlled using uni-polarity (a narrow and wide pulse having the same amplitude polarity) and bipolar (opposite amplitude polarity narrow pulses) programming. These programming characteristics make the PCMO well suited for use in memory cells and resistor RAM (RRAM) applications. These memory cell devices typically employ at least one electrode made, at least partially, from a noble metal, adjacently located to the PCMO memory resistor material.
There are many methods used for PCMO thin film deposition, such as physical vapor deposition (PVD), metalorganic chemical vapor deposition (MOCVD), and spin-coating. Of the three, spin-coating is one of the best candidates for the large scale manufacturing, as it is a relatively low cost, easy process.
FIG. 1 is a drawing depicting a PCMO film, formed using a conventional spin-coating process, overlying a Pt electrode (prior art). As can be seen in the figure, a void is formed in the interface between the PCMO and Pt layers. The problem is likely a result of the poor wetting properties of the PCMO spin-coating solution on the Pt surface. These voids are extremely detrimental to performance of RRAM devices. The voids encourage the formation of shorts between the top and bottom electrodes and degrade (increase) the leakage current. Further, the voids may result in the PCMO film being peeled from the Pt substrate during subsequent fabrication processes, such as during a chemical mechanical polish (CMP) step.
It would be advantageous if PCMO film could be consistently formed, without voids, on a noble metal substrate.
It would be advantageous if the above-mentioned void-free PCMO film could be formed using a spin-coating process.